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Dec 15th, 2006

Help to get time zone between GMT & new york

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Please can anyone help me to get the time zone between GMT & New York including the daylight saving.

I am able to get the timezone between GMT & localtime including the daylight saving. My program goes like this

c Syntax (Toggle Plain Text)
time_t t = time(0);
struct tm* data;
data = localtime(&t);
data->tm_isdst = 0;
time_t a = mktime(data);
data = gmtime(&t);
data->tm_isdst = 0;
time_t b = mktime(data);
int gmtoffset = (a - b)/3600;
time_t t = time(0);
struct tm* data;
data = localtime(&t);
data->tm_isdst = 0;
time_t a = mktime(data);
data = gmtime(&t);
data->tm_isdst = 0;
time_t b = mktime(data);
int gmtoffset = (a - b)/3600;

But I am not able to New York local time. Thanks a lot in advance.

Last edited by ~s.o.s~; Dec 15th, 2006 at 12:53 pm. Reason: Added code tags learn to use them yourself.

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jobra

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Dec 15th, 2006

Re: Help to get time zone between GMT & new york

Why not subtract the difference in hours between GMT and New York from the hour in GMT, adjusting for MN when necessary? I believe hour is one of the members of the tm struct.

Lerner

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Dec 15th, 2006

Re: Help to get time zone between GMT & new york

what operating system? There are no standard C or C++ functions to do that. If you are using MS-Windows you can call the win32 api function GetTimeZoneInformation()

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Dec 15th, 2006

Re: Help to get time zone between GMT & new york

I am using Linux operating system. so I dont think I can call the win32 api function GetTimeZoneInformation().

Is there a possibility to get current time in new york each time the program runs, so that i can calculate the timezone??

jobra

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Dec 15th, 2006

Re: Help to get time zone between GMT & new york

EST is GMT - 5. So if you know what time zone your program is running in then adjust accordingly. use gmtime() then subtract 5 hours for eastern.

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Dec 15th, 2006

Re: Help to get time zone between GMT & new york

Beaten to the punch, but I might have said something like this...

C Syntax (Toggle Plain Text)
#include <stdio.h>
#include <time.h>
 
int main (void)
{
   time_t t = time(0);
   if ( t != (time_t)-1 )
   {
      struct tm* data = gmtime(&t);
      if ( data )
      {
         data->tm_hour -= 5 + data->tm_isdst;
         t = mktime(data);
         if ( t != (time_t)-1 )
         {
            char buffer[32];
            if ( strftime(buffer, sizeof buffer, "%X", data) )
            {
               printf("NY time = %s\n", buffer);
            }
         }
      }
   }
   return 0;
}
 
/* my output
NY time = 00:36:52
*/
#include <stdio.h>
#include <time.h>

int main (void)
{
   time_t t = time(0);
   if ( t != (time_t)-1 )
   {
      struct tm* data = gmtime(&t);
      if ( data )
      {
         data->tm_hour -= 5 + data->tm_isdst;
         t = mktime(data);
         if ( t != (time_t)-1 )
         {
            char buffer[32];
            if ( strftime(buffer, sizeof buffer, "%X", data) )
            {
               printf("NY time = %s\n", buffer);
            }
         }
      }
   }
   return 0;
}

/* my output
NY time = 00:36:52
*/

Of course, I don't know whether or not gmtime will give you the correct Daylight Savings Time for New York. But it's a start.

Last edited by Dave Sinkula; Dec 15th, 2006 at 1:34 am. Reason: Updated time and added disclaimer.

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Dec 15th, 2006

Re: Help to get time zone between GMT & new york

Thanxs a lot for your reply. I understand. Right now I am using the same idea what you have explained in my program.

But what I want to make is automatically generate the timezone as the EST changes to EDT (daylight saving). I dont want to go to the program each time when EST changes to EDT to change the variable from -5 to -4. Hope I have made it clear.

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Re: Help to get time zone between GMT & new york

First I'd convert GMT to EST. Then I'd see if the EST date falls withing the interval that DST starts and ends. If so, then I'd add an hour to EST time to convert from not DST to DST. Or something like that. You may need to fine tune it to the hour that DST starts in addition to the date that DST starts, but I think you get the picture.

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Dec 17th, 2006

Re: Help to get time zone between GMT & new york

UNIX only:

C Syntax (Toggle Plain Text)
getenv("TZ");
getenv("TZ");

will return the timezone setting. The result is in the form
xxxNxxx, example MST7MDT. TZ has to be set for localtime() to return the correct time. MST is GMT +7. If TZ is not set the system is running GMT by default. Assuming time has been set.....
NY is EST5EDT. It's GMT+5.

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Dec 18th, 2006

Re: Help to get time zone between GMT & new york

Thanxs a lot. So you mean to say that this works only in unix. How about in Linux?? If it can be used in Linux, can you elaborate by giving an example code?? Thanxs once again.

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